Prolonged outburst (6)
I believe the answer is:
tirade
'prolonged outburst' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tirade that I've seen before include "Verbal onslaught" , "Vocal abuse" , "Intemperate outburst" , "Verbal broadside" , "String of invectives" .)